The present invention relates to an apparatus and a method for reproducing a multi-layer disc which has, for example, a first layer containing a recorded audio signal of a first quality and a second layer containing a recorded audio signal of a second quality higher than the first quality.
There is currently proposed a novel type of optical disc termed DVD (Digital Versatile Disc) greater in capacity than the known compact disc (hereinafter referred to as CD).
On a DVD which is an optical disc of 12 cm in diameter, information is recorded at a track pitch of 0.8 .mu.m narrower than an ordinary track pitch of 1.6 .mu.m employed on the conventional CD, and the wavelength of a semiconductor laser is changed from 780 nm on the CD to 630 nm, and the EFM (Eight-to-Fourteen Modulation) adopted for the CD is improved to consequently realize high-density recording which corresponds to information of approximately 4G bytes on one side of the disc.
Relative to such DVD, a multi-layer structure having two recording layers is lately proposed.
As disclosed, for example, in U.S. Pat. No. 5,706,263 filed on Mar. 26, 1997, the present applicant proposed a high-quality digital audio disc having a multi-layer structure where a 16-bit digital audio signal sampled at a frequency of 44.1 kHz is recorded in one layer, while a 1-bit quantized digital audio signal is recorded in another layer after being processed through .SIGMA..DELTA. modulation at a very high sampling frequency of 2.842 MHz which is 16 times the above frequency of 44.1 kHz.
The contents of signals to be recorded in such individual two layers are mutually the same (e.g., same music piece). Therefore, data of the same contents are recorded as normal-quality data of a CD level in one layer while being recorded as higher-quality data in the other layer.
Since such a multi-layer disc has one layer containing a recorded 16-bit digital audio signal sampled at 44.1 kHz, it is reproducible by any of ordinary compact disc players available currently in the general market.
Further in any apparatus adapted for reproduction of both layers, signals are reproducible properly from the two layers, so that any of a multiplicity of compact discs diffused widely now can be reproduced and still the novel multi-layer disc mentioned above can be reproduced as well.
Any of compact discs available in general and the novel multi-layer disc are substantially the same in external appearance. And in one of the layers of the multi-layer disc, data is recorded in conformity with the format of a compact disc so as to maintain down-compatibility therewith, i.e., digital audio signal processed through sampling at 44.1 kHz, 16-bit quantization and EFM is recorded.
For the purpose of explanatory convenience in the following description, one layer containing recorded data of the CD format will be referred to as a CD layer, and another layer containing recorded 1-bit digital audio signal processed at a sampling frequency of 2.842 MHz through .SIGMA..DELTA. modulation will be referred to as an HD (High-Definition) layer.
In reproduction of such a multi-layer disc having both a CD layer and an HD layer, it is necessary in a reproducing apparatus to execute a discrimination between the layers for reproduction and to perform various control actions.
In order to meet the above requirement, if identifiers relative respectively to the two layers are preset in a TOC (table of content) formed as a management area, a discrimination between the layers may be rendered possible with facility. However, in case such identifiers are newly recorded, compatibility between a conventional compact disc and a CD layer of a novel multi-layer disc may fail to be attained with a resultant possibility of inconvenience in use, so that additional recording of such identifiers is not desirable.
Furthermore, there exists a problem that the user cannot recognize which of a compact disc and a multi-layer disc is loaded in the apparatus unless the user is conscious of the disc type when loading the same.
In addition, another problem is also existent in the point that, since the recorded content of a CD layer and that of an HD layer are mutually the same (e.g., music piece or the like as a program), it is difficult to judge, by mere listening to the reproduced sound, which of the layers is being currently reproduced.